Hopefully, one of these procedures will resolve your problems with IE.
If that doesn't work, try a clean boot http://support.microsoft.com/kb/929135. If the problem goes away
then it's just a matter of tracking down the culprit causing the problem. Follow the procedures in the article. Once found, delete, remove, deactivate, or uninstall it. Once done be sure to reset Vista back to normal status as explained in the procedures.
If the problem occurs in clean mode then just restore the system to normal status and reboot - this solution is not going to work.
Boot into Safe mode with networking and see if the problem occurs there. Either result helps us narrow down the search for the cause.
If that doesn't work, you may be infected with malware. Try to run anti-malware programs (in safe mode with networking if
necessary). To fix this problem (if it is a problem) download, install, and run the following two programs:
http://www.safer-networking.org/en/index.html. Also update and run a full scan using whatever security software you currently have installed.
Ultimately, if none of that works, uninstall IE9 and then re-install it to see if that fixes the problem. But let's be sure we do it the right way:
Next, lets make sure we've covered any problems such as missing prerequisites and such. Follow the instructions in this article:http://support.microsoft.com/kb/2409098.
Ignore the recommended download locations in the article and use the one that follows:
Once the download is complete, go to your desktop and the installation program icon should be there. Right click on it and click on Run as Administrator (even if you are already logged in as an administrator) and it should proceed with the installation
(this process sometimes helps with installations). Reboot when done and when you return, hopefully IE9 will be installed and working.